For me: the Out Run OST. Everyone listens to and praises Nintendo OSTs or Square Enix, but Out Run is something else. I have rarely listened to video game music that catchy.
That's why I think they're great. Good standalone songs put in a fitting context.
Bought and played NFS heat recently. Game was surprisingly good, music, however had too much hip-hop/pop and stuff like that for my taste so that was disappointing.
Really basic, but Mario Kart DS specifically. The gameplay does not do it for me, but the way it sounds coming out of the DS's Speakers sounds amazing. Though, Mario Kart 64 & Wii are probably really close for me out of sheer nostalgia.
My shortlist is probably WipEout Pulse (I love how that entire series feels like a game made out of electronic music, the same way Doom is made out of metal), WipEout 2048 (for the same reason, but I played it even more), Forza Motorsport 2 (cuz it had a huge influence on my taste at a very young age), and then maybe Gran Turismo 5?
While not a racing game in the traditional sense, the soundtrack for I Am Your Beast is what cocaine sounds like. Listen to Negative Time without vibing, I bet you can't.